Multiple applications make use of field-effect power-transistors of the normally open type that are used in switching. Many applications make use of d.c. voltage, for example, for automobile traction. NMOS power transistors are often used for safety functions, for example, to isolate a connection terminal from a voltage source. When such a power transistor is confronted with a short circuit fault, the voltage source may apply a short circuit current that very rapidly reaches an elevated amplitude. To avoid the serious overheating connected with such a current, it is essential to detect a fault of the transistor in a very short time in order to implement safety measures, in particular, to control the opening of other transistors or prevent their closing.
Among the known fault detection devices, no solution at a reasonable cost has been identified to detect sufficiently rapidly and reliably a fault in a field effect power transistor.